In coupling separate optical fibers in an optical fiber cable for light transmission, coupling efficiency is achieved in measure corresponding to the level of three-dimensional alignment of the fibers. The fibers are elongate, comprising light-transmitting cores and a cladding having an index of refraction less than that of the core. The fiber in the cable is surrounded by a plastic buffer material and an outer plastic jacket. In typical preparation for connection, the jacket and buffer are stripped from each fiber to expose selected fiber lengths. The fibers are then disposed in fixed position in individual connector parts to be joined in such three-dimensional registry as to impart desired alignment to the fibers.
Misregistration can occur in any one of the three axes of alignment, based on tolerances applicable to each of the matable connector parts. Any of X or Y-axis misalignments will give rise to substantially lesser coupling efficiency than will a further coupling loss geometric parameter, namely, endwise spacing along the Z-axis between aligned fibers. Various such connectors employing matable parts holding fibers in alignment are set forth in the statement filed herein pursuant to 37 CFR 1.97 and 1.98.
Beyond the above described efforts, the optical element coupling art has seen alternative structure, wherein coupling is achieved, by fiber-to-fiber-interface through a common unitary body, i.e., as is set forth in U.S. Pat. No. 4,119,362, entitled "Optical Fiber Connector Using Opposed Lenses". In the referenced patent, a transparent coupler block is secured within a connector and defines, at opposed sides thereof, cavities having surfaces of revolution which are semispherical at the cavity interior. Tangential to the semispherical surfaces are frustro-conical surfaces which extend to the open ends of the cavities. Full line contact with the fiber end face is provided by either abutment of the fiber with the semispherical surface or with the frustro-conical surface. A self-centering effect is said to be achieved.
In applicants' view, optical element termination in either of the foregoing two described approaches can provide alignment and coupling results and efficiencies in lesser level than that presently desired by the art. Thus, misalignments in the first-described connecting approach are noted to be common without precise machining and control of parts and tolerances. The second approach is considered to give rise to misalignment where the entirety of the fiber end face does not define an end surface having a perfectly round periphery or circumference.